1. Field of the Invention
This invention relates to the rotational positioning of a chuck for supporting a semiconductor wafer and, more particularly, to a two-stage rotational positioning chuck assembly with increased rotational capabilities for successive mask layer registration of odd-shaped, odd-sized semiconductor wafers supported by the chuck assembly.
2. Description of the Background Art
Integrated circuits and other miniaturized electronic component formed on semiconductor wafers, such as silicon, are important in today's electronic industry. Fabrication of such integrated circuits and other electronic components is normally effected by supporting a semiconductor wafer in a machine whereby the wafer may be subjected to photolithographic steps. More specifically, the silicon wafer is first coated with a photoresist layer and then exposed to x-rays, ultraviolet or other electron or photon rays in a pattern determined by a preselected mask. When the process is repeated with the wafer being exposed through plural but correlated masks for successive mask layer registration, the desired integrated circuit or other electronic component is formed on the wafer.
One typical machine capable of sequentially exposing patterns in registration onto silicon wafers is the 6000 Series DSW machine manufactured by GCA Corporation, IC Systems Group of Bedford, Massachusetts Such machines, however, can only be as accurate as the initial positioning or alignment of the wafer on the chuck of the machine. Initial alignment is effected by an operator moving the chuck and its supported wafer through the use of the joy stick or other mechanical mechanism capable of moving the chuck plate and wafer in a first or x direction, in a second perpendicular or y direction, and in a third or theta rotational direction about the axis of the chuck and wafer. During the moving of the chuck and wafer, the operator visually observes and aligns two prepositioned marks or keys on the wafer through optical columns in the machine. When the operator properly moves the chuck and wafer to align the keys, the wafer will then be properly aligned within the machine for processing.
A variety of commercially available machines are well suited for the initial alignment of silicon wafers manufactured to standard dimensions. A first or coarse alignment or positioning may be done automatically by taking advantage of the roundness of the wafer and well-defined flats formed in their edges. A spindle off-site of the chuck can rotate a wafer 360.degree. as a mechanical flat finder searches for the flat edge. Once it finds this flat edge, the wafer is loaded onto the chuck by an automatic wafer handler for the second or fine alignment. A second or fine alignment or positioning is then done mechanically and optically by precisely aligning the alignment keys on the wafer, which are spaced apart at a predetermined distance to the optical column. Manual loading of silicon wafers onto the chuck by placing the well-defined flat in contact with a wafer stop is not preferred because a) any initial misalignment of the wafer onto the chuck would increase the amount of time needed to do the fine alignment and would, therefore, increase wafer processing time and cost, and b) a microscope would need to be built into the optical column in order to do a first or coarse adjustment This would minimize the space available in the column for advanced optics.
Indium antimonide wafers are preferred over silicon wafers for certain electronic applications. These wafers, however, are fragile and must be handled with extreme care, for not only do they chip and break easily, but wafer handling also affects their electrical characteristics Therefore, any wafer handling as during alignment and processing must be minimized. One way is to replace the present wafer aligning mechanisms that require constant top and bottom surface contact with the wafer with new mechanisms which provide for backside contact only such as the DSW machine. The problem occurs in finding an aligner that can be used with indium antimonide or like wafers which are characterized by their odd-shapes and odd-sizes.
These wafers, because their shapes and sizes vary by ingot, are not susceptible to automatic positioning and alignment in machines and, therefore, must be mounted onto the chuck manually. Guides are of limited use in the coarse positioning of these wafers since in many cases there is not a well defined wafer flat or edge for coarse positioning purposes. Even so, x and y corrections can be easily made with existing aligners. However, movement in the critical theta direction is so severely limited that it is virtually impossible to align these wafers with the commercially available chucks. As a result, a new chuck of the present invention was designed and developed for use on the indium antimonide wafers.
In addition to the chuck positioning apparatus of the above-referred to 6000 Series DSW machine, the patent literature discloses other mechanisms for chuck and wafer positioning and alignment. By way of example, U. S. Pat. No. 3,685,117 to Wing; 3,969,004 to Schliemann and 4,544,311 to Husain disclose chuck positioning devices for use in association with mask alignment. In addition, U.S. Pat. Nos. 3,990,689 to Eklund; 4,066,943 to Roch; and 4,448,403 to Riessland disclose chuck positioners for testing purposes. All of these prior art devices require complex mechanisms for effecting chuck movement and are limited in their extent of rotational movement.
These and other advances in chuck assemblies for wafer alignment are commercially available and are described in the literature. All are noteworthy to one extent or another, but none achieves the objective of an efficient, accurate, convenient and inexpensive device to initially align semiconductor wafers in a machine for forming integrated circuits or similar electronic components thereon, the apparatus being particularly designed to accommodate the specific needs of odd-shaped, odd-sized wafers such as indium antimonide.
As illustrated by the great number of prior patents as well as commercial devices, efforts are continuously being made in an attempt to improve adjustable chuck assemblies to render them more efficient, accurate, convenient and economical in the positioning of semiconductor wafers. None of these previous efforts, however, provides the benefits attendant with the present invention. Additionally, prior methods and devices do not suggest the present inventive combination of component elements arranged and configured as disclosed and claimed herein. The present invention achieves its intended purposes, objects and advantages over the prior art devices through a new, useful and unobvious combination of component elements, with the use of a minimum number of functioning parts, at a reasonable cost to manufacture, and by employing only readily available materials.
Therefore, it is an object of this invention to provide an improved chuck assembly for efficiently, accurately, conveniently and economically positioning semiconductor wafers in machines for forming integrated circuits and other electronic components thereon.
It is another object of this invention to adjust the angular position of odd-shaped, odd-sized semiconductor wafers in fabrication machines over a wide range of rotation.
It is a further object of the invention to align indium antimonide semiconductor wafers in machines prior to processing.
Lastly, it is an object of the present invention to provide an improved chuck assembly, for use in machines capable of forming integrated circuits or the like on odd-shaped, odd-sized semiconductor wafers, for increasing the rotational adjustment capabilities of the chuck assembly and a semiconductor wafer supported thereon, the chuck assembly comprising a mounting ring having a circular configuration formed of a plate and a peripheral wall forming a circular recess extending from a surface of the mounting ring, a chuck plate having a circular configuration adapted to be received within the recess of the mounting ring, a lever extending radially from one edge of the chuck plate through an opening in the side wall of the mounting ring, an adjusting bracket secured to the exterior edge of the mounting ring, and a screw rotatably supported in a threaded aperture in the adjusting bracket and coupled to the lever whereby rotation of the screw will move the lever for adjusting the angular orientation of the chuck plate with respect to the mounting ring.
The foregoing has outlined some of the more pertinent objects of the invention These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention as defined by the claims taken in conjunction with the accompanying drawings.